Jimmy Stamp, a blogger at smithsonianmag.com wrote a partial history of headphones, looking all the way back to headphone origins during the 1890s. While it isn't an in-depth history, he still manages to comment on the Electrophone, as well as the developments in headphones during World War I from Nathaniel Baldwin, and the beginnings of Koss headphones.

I never knew that in-ears were developed that early and that such things were based off of a stethoscope-like design.

Didn't think that they made phones until around the 1930's after WWI, but it makes sense seeing that stereo was made near the end of the 19th century. Hard to think since I don't think of the 1800's as much of a technological century compared to the early 20th. Also never knew they were used in wars and had something practical that early.

As for the future, I'm not so sure. Wireless in-ears/buds/clip-ons might be next. As far as sound goes, only STAX has been able to make a come back to the top with sound and detail that rivals/surpasses the orpheus and other top tier phones. I'd imagine it as harder to go any further at this point. Mainstream companies are mostly there for profits (well it's a capitalistic world, and it's the world of business, so I can't expect much), and it seems like old-timer companies like Sony and Sennheiser (both respectable for me) have been following them which kind of bothers me.

I don't see any company as of the current going for anything higher at the moment, but it looks like they're shifting their marketing targets. I don't really see build quality going up, presumably because of costs. Since it's been heading towards the mainstream audience, and companies have been going portable with their amazing iDevice cables with buttons,the future will lie within portable phones. Specialized phones for us audiophiles will still exist, but it looks like the apex of detail/realism has been peaked. Prices look to only go higher and higher, too.

Already done. Yamaha released the YH-5M as a Japan-Only in-ear orthodynamic back in the 70's. They're incredibly rare, one person on this forum has them.

On-Topic: Great read, I enjoyed it.

Personally I think consumer headphones will continue sounding like **** and audiophile headphones will continue getting better. I also predict the arise of many companies charging $5000+ for their headphones. Thank you, Sennheiser.

Already done. Yamaha released the YH-5M as a Japan-Only in-ear orthodynamic back in the 70's. They're incredibly rare, one person on this forum has them.

On-Topic: Great read, I enjoyed it.

Personally I think consumer headphones will continue sounding like **** and audiophile headphones will continue getting better. I also predict the arise of many companies charging $5000+ for their headphones. Thank you, Sennheiser.

If you consider electrostatics as planars (which they technically are, just a different drive mechanism) then Stax has them.